174 research outputs found
All-Optical Manipulation of Electron Spins in Carbon-Nanotube Quantum Dots
We demonstrate theoretically that it is possible to manipulate electron or
hole spins all optically in semiconducting carbon nanotubes. The scheme that we
propose is based on the spin-orbit interaction that was recently measured
experimentally; we show that this interaction, together with an external
magnetic field, can be used to achieve optical electron-spin state preparation
with a fidelity exceeding 99%. Our results also imply that it is possible to
implement coherent spin rotation and measurement using laser fields linearly
polarized along the nanotube axis, as well as to convert spin qubits into
time-bin photonic qubits. We expect that our findings will open up new avenues
for exploring spin physics in one-dimensional systems
Molecular cavity optomechanics: a theory of plasmon-enhanced Raman scattering
The conventional explanation of plasmon-enhanced Raman scattering attributes
the enhancement to the antenna effect focusing the electromagnetic field into
sub-wavelength volumes. Here we introduce a new model that additionally
accounts for the dynamical and coherent nature of the plasmon-molecule
interaction and thereby reveals an enhancement mechanism not contemplated
before: dynamical backaction amplification of molecular vibrations. We first
map the problem onto the canonical model of cavity optomechanics, in which the
molecular vibration and the plasmon are \textit{parametrically coupled}. The
optomechanical coupling rate, from which we derive the Raman cross section, is
computed from the molecules Raman activities and the plasmonic field
distribution. When the plasmon decay rate is comparable or smaller than the
vibrational frequency and the excitation laser is blue-detuned from the plasmon
onto the vibrational sideband, the resulting delayed feedback force can lead to
efficient parametric amplification of molecular vibrations. The optomechanical
theory provides a quantitative framework for the calculation of enhanced
cross-sections, recovers known results, and enables the design of novel systems
that leverage dynamical backaction to achieve additional, mode-selective
enhancement. It yields a new understanding of plasmon-enhanced Raman scattering
and opens a route to molecular quantum optomechanics.Comment: Extensively revised and improved version thanks to the hard work and
constructive comments of a careful Referee. Includes Supplemental Materia
Heralded single phonon preparation, storage and readout in cavity optomechanics
We analyze theoretically how to use the radiation pressure coupling between a
mechanical oscillator and an optical cavity field to generate in a heralded way
a single quantum of mechanical motion (a Fock state), and release on-demand the
stored excitation as a single photon. Starting with the oscillator close to its
ground state, a laser pumping the upper motional sideband leads to dynamical
backaction amplification and to the creation of correlated photon-phonon pairs.
The detection of one Stokes photon thus projects the macroscopic oscillator
into a single-phonon Fock state. The non-classical nature of this mechanical
state can be demonstrated by applying a readout laser on the lower sideband
(i.e. optical cooling) to map the phononic state to a photonic mode, and by
performing an autocorrelation measurement on the anti-Stokes photons. We
discuss the relevance of our proposal for the future of cavity optomechanics as
an enabling quantum technology.Comment: Accepted for publication in Physical Review Letters. Added References
42,4
Preparation and decay of a single quantum of vibration at ambient conditions
A single quantum of excitation of a mechanical oscillator is a textbook
example of the principles of quantum physics. Mechanical oscillators, despite
their pervasive presence in nature and modern technology, do not generically
exist in an excited Fock state. In the past few years, careful isolation of
GHz-frequency nano-scale oscillators has allowed experimenters to prepare such
states at milli-Kelvin temperatures. These developments illustrate the tension
between the basic predictions of quantum mechanics that should apply to all
mechanical oscillators existing even at ambient conditions, and the complex
experiments in extreme conditions required to observe those predictions. We
resolve the tension by creating a single Fock state of a vibration mode of a
crystal at room temperature using a technique that can be applied to any
Raman-active system. After exciting a bulk diamond with a femtosecond laser
pulse and detecting a Stokes-shifted photon, the 40~THz Raman-active internal
vibrational mode is prepared in the Fock state with probability.
The vibrational state is read out by a subsequent pulse, which when subjected
to a Hanbury-Brown-Twiss intensity correlation measurement reveals the
sub-Poisson number statistics of the vibrational mode. By controlling the delay
between the two pulses we are able to witness the decay of the vibrational Fock
state over its ps lifetime at room temperature. Our technique is agnostic
to specific selection rules, and should thus be applicable to any Raman-active
medium, opening a new generic approach to the experimental study of quantum
effects related to vibrational degrees of freedom in molecules and solid-state
systems
Photon Antibunching in the Photoluminescence Spectra of a Single Carbon Nanotube
We report the first observation of photon antibunching in the
photoluminescence from single carbon nanotubes. The emergence of a fast
luminescence decay component under strong optical excitation indicates that
Auger processes are partially responsible for inhibiting two-photon generation.
Additionally, the presence of exciton localization at low temperatures ensures
that nanotubes emit photons predominantly one by one. The fact that multiphoton
emission probability can be smaller than 5% suggests that carbon nanotubes
could be used as a source of single photons for applications in quantum
cryptography.Comment: content as publishe
Mode-specific Coupling of Nanoparticle-on-Mirror Cavities with Cylindrical Vector Beams
Nanocavities formed by ultrathin metallic gaps, such as the
nanoparticle-on-mirror geometry, permit the reproducible engineering and
enhancement of light-matter interaction thanks to mode volumes reaching the
smallest values allowed by quantum mechanics. Although a large body of
experimental data has confirmed theoretical predictions regarding the
dramatically enhanced vacuum field in metallic nanogaps, much fewer studies
have examined the far-field to near-field input coupling. Estimates of this
quantity usually rely on numerical simulations under a plane wave background
field, whereas most experiments employ a strongly focused laser beam. Moreover,
it is often assumed that tuning the laser frequency to that of a particular
cavity mode is a sufficient condition to resonantly excite its near-field.
Here, we experimentally demonstrate selective excitation of nanocavity modes
controlled by the polarization and frequency of the laser beam. We reveal
mode-selectivity by recording fine confocal maps of Raman scattering intensity
excited by cylindrical vector beams, which are compared to the known excitation
near-field patterns. Our measurements allow unambiguous identification of the
transverse vs. longitudinal character of the excited cavity mode, and of their
relative input coupling rates as a function of laser wavelength. The method
introduced here is easily applicable to other experimental scenarios and our
results are an important step to connect far-field with near-field parameters
in quantitative models of nanocavity-enhanced phenomena such as molecular
cavity optomechanics, polaritonics and surface-enhanced spectroscopies.Comment: 23 pages, 11 figures (SI included
Molecular Vibration Explorer: an Online Database and Toolbox for Surface-Enhanced Frequency Conversion and Infrared and Raman Spectroscopy
We present Molecular Vibration Explorer, a freely accessible online database and interactive tool for exploring vibrational spectra and tensorial light-vibration coupling strengths of a large collection of thiolated molecules. The "Gold" version of the database gathers the results from density functional theory calculations on 2800 commercially available thiol compounds linked to a gold atom, with the main motivation to screen the best molecules for THz and mid-infrared to visible upconversion. Additionally, the "Thiol" version of the database contains results for 1900 unbound thiolated compounds. They both provide access to a comprehensive set of computed spectroscopic parameters for all vibrational modes of all molecules in the database. The user can simultaneously investigate infrared absorption, Raman scattering, and vibrational sum- and difference-frequency generation cross sections. Molecules can be screened for various parameters in custom frequency ranges, such as a large Raman cross-section under a specific molecular orientation, or a large orientation-averaged sum-frequency generation (SFG) efficiency. The user can select polarization vectors for the electromagnetic fields, set the orientation of the molecule, and customize parameters for plotting the corresponding IR, Raman, and sum-frequency spectra. We illustrate the capabilities of this tool with selected applications in the field of surface-enhanced spectroscopy
Bell correlations between light and vibration at ambient conditions
Time-resolved Raman spectroscopy techniques offer various ways to study the
dynamics of molecular vibrations in liquids or gases and optical phonons in
crystals. While these techniques give access to the coherence time of the
vibrational modes, they are not able to reveal the fragile quantum correlations
that are spontaneously created between light and vibration during the Raman
interaction. Here, we present a scheme leveraging universal properties of
spontaneous Raman scattering to demonstrate Bell correlations between light and
a collective molecular vibration. We measure the decay of these hybrid
photon-phonon Bell correlations with sub-picosecond time resolution and find
that they survive over several hundred oscillations at ambient conditions. Our
method offers a universal approach to generate entanglement between light and
molecular vibrations. Moreover, our results pave the way for the study of
quantum correlations in more complex solid-state and molecular systems in their
natural state
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